Japanese researchers monitoring the activity of giant jellyfish in Chinese waters are warning of a potentially historic and catastrophic invasion this year.
Marine surveys conducted in late June have revealed alarming numbers of Nomura’s jellyfish — massive creatures that grow up to 2 meters (6 ft 7 in) in diameter and weigh as much as to 220 kilograms (about 450 lbs) — lurking in the Yellow Sea and East China Sea. The researchers warn that ocean currents may bring swarms of the monster jellies to Japan, which has been plagued by similar invasions in recent years.
Between June 20 and 24, 2009, Japanese Ue’s team observed numerous specimens with umbrellas measuring 10 to 50 centimeters across, and they calculated an average distribution of 2.14 jellyfish per 100 square meters. This figure is more than 200 times higher than the 0.01 jellyfish per 100 square meters observed in the same region in 2008. It is also nearly triple the 0.77 jellyfish per 100 square meters observed in 2007, when the fishing industry in the Sea of Japan suffered widespread damage.
Nomura’s jellyfish typically bloom in Chinese waters in spring, and they mature into adults as ocean currents slowly carry them north. By July, when the first swarms reach Tsushima (just north of the southern island of Kyushu), many jellyfish are as large as sumo wrestlers. At this size, it only takes about 5 or 10 of them to destroy a commercial fishing net.
In addition to damaging nets, the giant jellyfish are blamed for killing other fish with their venom, lowering the quality and quantity of catches, increasing the risk of capsizing trawlers, and stinging fishermen.